1. Field of the Invention
The present invention relates to an optical disc, an optical disc drive for replaying and recording information from and to the optical disc, and information apparatuses and systems using the optical disc and the optical disc drive, such as a computer, a disc player, a car navigation system, an optical disc recorder and a vehicle. In addition, the present invention relates to a method for replaying information and an integrated circuit.
2. Description of the Related Art
Digital versatile discs (DVDs) have been known as optical discs capable of storing data with high capacities, since digital information can be recorded in these digital versatile discs with recording densities which are about 6 times those of compact discs (CDs). In recent years, there has been a need for optical discs having larger capacities, along with the increase of amounts of information to be recorded in optical discs. In order to increase the capacity of an optical disc, it is necessary to reduce the size of a light spot formed by light directed to the optical disc when information is recorded to the optical disc or information recorded in the optical disc is replayed, for increasing the density of information recorded therein. The reduction of the size of the light spot can be realized by employing a light source which emits laser light with a shorter wavelength and employing an objective lens with a greater numerical aperture (NA).
For DVDs, a light source with a wavelength of 660 nm (red) and an objective lens with a numerical aperture (NA) of 0.6 have been employed. Further, for BDs (Blu-Ray Discs) which have been already commercially available, a blue laser with a wavelength of about 405 nm and an objective lens with an NA of 0.85 have been employed, which have realized a recording density which is five times that of existing DVDs.
Further, as optical discs which require blue lasers, there are HD-DVDs which require an objective lens having an NA of 0.65 and have been commercially available.
A DVD is an optical disc including transparent base materials with a thickness of 0.6 mm which requires a laser light source with a wavelength of about 660 nm for recording or replaying, also requires an objective lens with a numerical aperture NA of 0.60 and includes recording layer(s) each having a recording capacity of about 4.7 GByte. A DVD is constituted by two transparent base materials with a thickness of 0.6 mm which are attached to each other and thus has a total thickness of 1.2 mm which equals to that of a CD.
A BD is an optical disc including a transparent base material with a thickness of about 0.1 mm which requires laser light with a wavelength of about 405 nm for recording or replaying, also requires an objective lens with a numerical aperture NA of 0.85 and includes recording layer(s) each having a recording capacity of about 25 GByte. A BD is constituted by a disc substrate with a thickness of 1.1 mm, recording layers provided on the disc substrate and a transparent cover layer with a thickness of 0.1 mm which covers the recording layers and has a total thickness of 1.2 mm which equals to that of a CD. Recording and replaying information on and from a BD is performed by converging blue laser light on the recording layers through the transparent cover layer with a thickness of 0.1 mm, using an objective lens with a numerical aperture of 0.85. The increase of the coma aberration caused by the use of laser light with a shorter wavelength and an objective lens with a greater NA is suppressed by setting the thickness of the transparent cover layer in a BD for passing the laser light therethrough to a smaller thickness of about 0.1 mm.
On the other hand, an HD-DVD is an optical disc which requires an objective lens with a numerical aperture NA of 0.65, includes recording layer(s) each having a recording capacity of about 15 GByte, is constituted by two transparent base materials with a thickness of 0.6 mm which are attached to each other and thus has a total thickness of 1.2 mm which equals to that of a CD.
As such optical discs, there are three types of optical discs, which are replay-only type optical discs which have prepits as recording layers, write-once type optical discs which include dye layers as recording layers, and rewritable type optical discs which include phase-change layers as recording layers.
As described above, there are optical discs with various structures, such as CDs, DVDs, BDs, HD-DVDs. The characteristic of the optical discs is that these optical discs can be inserted into and ejected from apparatuses so as to enable recording and replaying information on and from various types of optical discs. Accordingly, it is desirable that an apparatus for replaying or recording information from and to optical discs is adapted to receive various types of optical discs, determine the types of them and properly perform focusing and groove-tracking controls thereon for replay information therefrom.
A method for distinguishing between a CD or a DVD is disclosed in JP-A No. 10-55602, for addressing the aforementioned need.
FIG. 11 is a flow chart briefly illustrating the optical-disc distinguishing method described in JP-A No. 10-55602.
If a command for replay of an optical disc is output (#101), then the numerical aperture (NA) of an objective lens for converging light on the optical disc is set to a certain value (#102), and the objective lens is moved in the direction of an optical axis by an actuator (#103). At this time, the type of the optical disc is determined, based on detection signals such as focus error signals output from an optical head device (#104).
If this determination was a first determination (NO in #105), the value of NA is switched (#106) and, thereafter, the objective lens is moved, again, in the direction of the optical axis by the actuator. At this time, the type of the optical disc is determined, based on detection signals such as focus error signals output from an optical head device. After the second determination is completed (YES in #105), it is determined whether or not the results of these determinations are the same (#107).
If they are the same (YES in #107), then the value of NA is set according to the result and, then, replay of the optical disc is performed (#108). If the results of the two determinations are different from each other (NO in #107), an alarm is generated (#109).
Similarly, JP-A No. 10-241268, JP-A No. 2002-117534, JP-A No. 2001-202680 and the like disclose methods for distinguishing the type of an optical disc.
JP-A No. 10-241268 discloses a method which provides light sources for red light and infrared light in an optical head device, causes them to emit light, determines the reflectivity of an optical disc and, from the result thereof, determines the type of the optical disc.
JP-A No. 2002-117534 discloses a method which determines the type of an optical disc, using tracking error signals detected by a method called a differential phase detection (DPD) method. In this case, tracking error signals are signals indicative of the deviation of a converged spot from the center of rows of pits and the center of track grooves in the optical disc. In the method disclosed in JP-A No. 2002-117534, the type of an optical disc is determined, by observing the change of tracking error signals in cases where pulse signals for use in detecting DPD are limited to signals with lengths equal to or less than a certain length.
Further, JP-A No. 2001-202680 discloses a method which determines the type of an optical disc, by observing the ratio of information signals to the amount of light reflected by the optical disc, namely the modulation degree of information signals.